Method of joining tubular member and annular parts

ABSTRACT

A joint structure of a metallic tubular member and metallic annular parts, the annular parts being joined to the outer periphery of the tubular member as in a camshaft. Each of the annular parts has around its inner periphery at least one serrated portion which cuts into the outer periphery of the tubular member when they are joined, the annular part also having a planar portion facing another portion of the tubular member in such a manner that substantially no pressure is exerted on the planar portion of the annular part. 
     A method of making such structure involves positioning of the tubular member is required in relation to the annular parts, as by use of a split die, and then forcing into the tubular member a pressing member to expand the tubular member so that the serrated portions cut into the outer periphery of the tubular member.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to the structure of a joint between a metallictubular member and a metallic annular part and a method of joining them,especially a joint structure and a method of joining a tubular memberand annular parts which are designed to constitute a hollow machinecomponent such as particularly a hollow cam shaft and a cam or camsthereon.

The use of hollow structures for machine components such as the camshaft in an internal combustion engine has become common recentlybecause of the strong demand for savings in material and the weightreduction of such components. As a means for achieving this, a techniqueis known according to which annular parts such as cams are mounted inposition on a tubular member prepared in advance, and then the tubularmember is expanded to join them.

Japanese Patent Publication No. 21,299/71 discloses a method in which atubular member (a shaft tube) is passed through heated split cam andjournal combinations (each cam having a shaft hole with splines), andthen the shaft tube is expanded by a pressing member (die) to joint theannular parts securely to the shaft tube. With this method, however,since splines are formed along the full length of each cam and journaland the shaft tube is expanded after is has been forced into the parts,the shaft tube inevitably stretches axially to cause bending or anonuniform wall thickness of the tube, so that it is impossible to jointhe parts (cams and journals) securely and correctly in the specifiedpositions. It is also extremely difficult to fix the cams in theirspecified positions by making allowance for possible elongation of theshaft tube. This method, therefore, can not be applied to mass producedmachine components.

A method has also been made known by Japanese Patent Publication No.506/81 in which a shaft tube is forced through splined shaft holes ofcams and then only the portion of the shaft tube corresponding to thesplined section of each cam is expanded outward to obtain a securejoint. This method also has a low reliability, especially in respect ofpull-out force, because engagement is provided at only a few places, andit also requires specific tools for splining, etc., and thus has a lowproductivity.

The present invention has solved these problems. It has for its objectthe provision of a structure for joining annular parts securely andaccurately to a tubular member, and a method of forming such structure.

In order to attain the object of this invention, at least one serratedportion is provided on the inner periophery of each annular part, theserrated portions being designed to cut or bite into the outer peripheryof a tubular member to which the annular parts are joined, each of theannular parts also having a planar portion facing other portions of thetubular members (portions that are not cut into), designed so thatsubstantially no pressure is exerted on the planar portions of theannular parts when they are joined to the tubular member, and then saidtubular member is deformed plastically and expanded to effect thedesired joining of the annular parts and tubular member within specifieddimensional tolerances.

An embodiment of this invention will be described below with referenceto the accompanying drawings which illustrate the embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a frontal elevation view of a tubular member, such as a camshaft, having annular parts, such as cams, thereon, being partiallysectioned and partially enlarged, to provide a component in accordancewith and embodying the invention;

FIGS. 2 and 3 are partially sectioned perspective views of the annularparts of the components of FIG. 1;

FIG. 4 is a cross sectional view showing the joining process of thepresent invention; and

FIG. 5 is a schematic illustration of conditions obtaining during thejoining process.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a section of the principal parts of a cam shaft comprising atubular member with annular parts secured thereto. In the drawing, theannular parts, that is, a journal 1 and a cam 2 in the embodiment shown,are disposed and fixed in position with a specific spacing therebetweenonto the outer periphery of a tubular member which is a shaft tube 3 inthis embodiment. In the journal 1 and cam 2, as shown in FIGS. 2 and 3,a series of serrated protuberances 11, 12, 21, 22 are formed annularlyby machining or other means along both edges of the hollow portions (theinner peripheries) thereof. There are planar portions 13, 23 positionedbetween these series of protuberances 11, 12, 21, 22 facing thecorresponding portions of the outer periphery 32 of the shaft tube 3.These protuberances 11, 12, 21, 22 cut perfectly into the shaft tube 3in such a manner that substantially no pressure is applied to theseplanar portions of the annular parts when they are joined to the tubularmember.

The conditions of joining the journal 1 and cam 2 will now be describedmore concretely with reference to FIGS. 4 and 5. First, the requirednumber of journals 1 and cams 2 are arranged at suitable spacings fromeach other and are held in position between a lower die A and an upperdie B of a split die, and then a shaft tube 3 is passed through thehollow portions in each of the journals and cams so that the foremostend 31 of the shaft tube 1 butts against and is supported by an end faceC. An important design feature of this invention is the construction ofthe journals 1 and cams 2 so that the inner diameter φ₁ of the serratedportions (the distance from end of one protuberance to the end of thediametrically opposite protuberance) is substantially equal to orgreater than the outer diameter φ₂ of the shaft tube 3 while the innerdiameter φ₃ of the planar portions 13, 23 between the serrated portions11 and 12, and 21 and 22 is slightly greater than the proposed outerdiameter φ₄ of the expanded tube which can be determined during thedesign stage. With the annular parts thus positioned under normaltemperature conditions, a pressing member (punch) 4 having a probeportion 41 and an enlarged portion (tube-expanding portion) 42 is forcedinto the shaft tube 3 in the direction indicated in the drawings. Thisdeforms the shaft tube 3 plastically and expands it outward, making theserrated protuberances 11, 12, 21, 22 to cut into said shaft tube 3.Thus the annular parts are secured to the shaft tube 3 by the shearingforce and clamping force provided thereto. The outer diameter φ₂ and thedimensions of the serrated portions 11, 12, 21, 22 and the planarportions 13, 23 are set as appropriate in advance so that no deformingpressure is exerted on the planar portions 13, 23, so that although theplastically deformed material fills the spaces in the planar portions13, 23, plastic deformation of the tubular member is checked by nothingbut the serrated ridges 11, 12, 21, 22, so that the shaft tube 3 remainssubstantially free of any action that would cause unevenness in the wallthickness, bending or axial elongation.

According to the results from test pieces, when four journals made ofNiCrMo steel were arranged equidistantly from each other on a shaft tubeof at least 100 mm made of an ordinary structural steel (SS 41), theycould be joined securely to the shaft tube with the same accuracy aswhen the annular parts were first arranged in a split die with theirouter peripheries clamped, even though the serrated protuberances on thearranged annular parts were positioned offset by a substantial amount(about 0.2 mm) from the theoretical center relative to the outerperiphery which served as a positional reference. The axial displacementbetween the annular parts was as small as only about 0.01 mm in thelongest section, and the total elongation of the shaft tube was limitedto only about 0.01 mm. Thus, annular parts could be securely joined to ashaft tube with a high accuracy with no bending or unevenness of wallthickness, and it was confirmed that they could well withstand practicalusage.

In the above embodiment, the serrated protuberances were provided aroundthe full circumference of both ends of the inner periphery of eachannular part, but they could be provided at only one end of the innerperiphery, or at the center, or near the center of the inner periphery,or at two or more such places. Provision of at least one array ofserrated protuberances is the minimum requirement. Also, while in theabove embodiment the engagement protuberances are formed as a series offine, continuous serrated prongs, they may be replaced with knurls orother forms of protuberance which can readily cut into the tubularmember to provide a secure joint between the tubular member and theannular part. It is desirable that the protuberances have a hardness atleast equal to that of the tubular member. The punch may not necessarilybe of a press-in type; it may be of a type in which a ball is pulledout. Such a type is also capable of making a straight drive operationand can well obtain the object of this invention.

In the above embodiment, the adaption of the invention to a cam shafthas been discussed, but the invention can be applied just as well togear wheels or other machine parts if such parts are annular in form andare designed to be joined to a tubular member.

According to this invention, as described above, a tubular member (shafttube) is plastically deformed while being pressed by serrated portionsof an annular part when the tube is expanded, but no pressure acts on aplanar portion of the annular part, so that well-balanced plasticdeformation is performed and the annular part provides almost noinfluence of unevenness of wall thickness, bending or elongation of thetubular member. Also, since the outer periphery of the tubular member isonly clamped by the serrated portions, no high pressure is required forthe pressing member. Further, since the annular parts are all joined atnormal temperatures, the products are free of any effects of heat andhence no temperature control is required. Thus the desired joint can beaccomplished rationally, easily, and accurately.

Although the foregoing includes a description of the best modecontemplated for carrying out the invention, various modifications arecontemplated.

As various modifications could be made in the constructions and methodsherein described and illustrated without departing from the scope of theinvention, it is intended that all matter contained in the foregoingdescription or shown in the accompanying drawings shall be interpretedas illustrative rather than limiting.

What is claimed is:
 1. A method of joining metallic annular parts to theouter periphery of a separately made metallic tubular member whichcomprises passing the tubular member through the annular parts each ofwhich has two spaced annular serrated engagement portions around itsinner periphery, positioning said tubular member as required in relationto said annular parts, and then expanding said tubular member internallyby forcing thereinto a pressing member having a diameter larger than theinner diameter of said tubular member in such a manner thatsubstantially no pressure is exerted on a cylindrical surface betweentwo spaced annular serrated portions on the inner periphery of each ofsaid annular parts while imparting a shearing force and a clamping forceto the outer wall of said tubular member to obtain a plasticallydeformed joint between said tubular member and said annular parts. 2.The method according to Claim 1 wherein the expansion of the tubularmember is performed by clamping the outer periphery of each annularpart.